It is the aim of the proposed study to examine the therapeutic potential that attaches to the observed ability of clinically active anticancer agents and of cell-derived factors to induce the in vitro differentiation of various tumor cell lines. Because this process is initiated at drug concentrations that are minimally or noncytotoxic, greater selectivity may be achievable than is possible with currently used maximally tolerated drug doses. This concept will be evaluated in vivo, using two murine myeloid leukemia cell lines, M1 and RF/UM which, respectively, proliferate i.p. and systemically, and are sensitive to treatment with anticancer agents. Drug and factor concentrations that are minimally or non-toxic to the host will be employed and treatment schedules are to be devised capable of providing maximal differentiation induction. Parallel studies are to be carried out in vitro to determine whether drug treatment renders leukemic cells sensitive to differentiation induction by natural factors and whether such treatment affects factor production itself. Mechanistic studies are projected, aimed at elucidating the molecular basis of drug- and factor- induced differentiation. Since the transition from proliferation to differentiation occurs within hours after treatment, the early changes in cellular protein and mRNA patterns that accompany this transition are to be determined by two-dimensional gel electrophoresis of the radiolabelled macromolecules. Because drug-induced differentiation occurs after inhibition of DNA synthesis and/or function, the nature of differentiation-associated gene expression is to be assessed by determining whether it involves new transcription or translation of pre-existing mRNA. In contrast, tetradecanoylphorbol ester and natural differentiation factors induce maturation without inhibiting DNA synthesis, and their effect appears mediated via membrane-associated events. These will be examined by determining the modification of membrane proteins the agents bring about. This experimental approach is expected to provide a meaningful assessment of the role differentiation might play in cancer therapy.
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